Practice_Problems_v1 - Question 1 Anisotropic Etching a....

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Question 1 Anisotropic Etching a. Using law of cosines to calculate the angle between the <100> and the <111> crystal plane. b. In class we discussed the technique to obtain two different cavity depths using anisotropic etching by using the <111> etch rates to be finite. In this problem you will design a mask to obtain two cavities in a 500 micron wafer, one that goes through the wafer, and another that goes to half the wafer thickness. The top dimensions of the through-wafer cavity should be 500X500 microns. Assume that the <100>/<111> etch rate ratio is 300, and once the <111> planes intersect at the bottom, the resulting protruding pyramids etch instantaneously (infinitely fast). Your mask should look like one open square and one grill-like mask. c. With a certain etchant, the etch selectivity between the {100} and {111} planes is 300:1, not infinite. Therefore, the sidewalls of a pit etched in a (100) wafer will be very close to the {111} planes but not exactly parallel to them. (a) What angle do they really make? (b) What etch ratio would be needed to make 45° sidewalls? Question 2. State the main advantages and disadvantages of LPCVD compared to PECVD thin film deposition. Question 3.
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This test prep was uploaded on 02/22/2008 for the course ECE 4320 taught by Professor Bhave during the Fall '07 term at Cornell University (Engineering School).

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Practice_Problems_v1 - Question 1 Anisotropic Etching a....

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